Iron Mountain's returning CEO has moved quickly to reach an accommodation with activist investor Elliot Management, being willing to sell-off the digital business, close unprofitable international operations, return cash to shareholders, and evaluate becoming a REIT.
Scenting that stockholder opinion was in line with that of …

They are....

If I remember correctly all their secure storage facilities mean that they actually are the owner of a massive amount of real-estate, enough to qualify them as a REIT. They can still do their core business, even if they change corporate types...

Not completely crazy

I believe the proposal is to create a REIT to own the buildings (and occasional iron mine) and an operating company to actually run the business. The operating company then pays rent to the real estate company. The overall structure has benefits due to how REITs are taxes. I would imagine that the bulk of the cost of running records storage is in the real estate. Certainly all of the investment is in building warehouses that can store 1+ million cubic feet of paper.